let the charges of washer = x ..
charges of dryer is three times than x = 3x
as we know their addition is 600 so
x + 3x = 600
4x = 600
dividing 4 on other side we get
x = 600 / 4
x = 150..
charges of washer = x= 150 dollars
charges of dryer = 3x= 3 (150) = 450 dollars
